If a memory device is going to fail, the probability that it will fail is greatest in the periods of initial usage, known as infant failure, and in a period a number of years after extended usage, known as wear-out. In order to eliminate the sale of devices that would fail during the initial usage period, the devices are rigorously stressed for a period, which will simulate the infant failure period, known as burn-in.
Burn-in and component stress times can become quite excessive with the advent of larger and larger memory devices. Greater voltages and higher ambient temperatures are often used to speed up the burn-in and stress test processes, but further reduction in burn-in and stress test times is still necessary.
A common method of burning-in and stress testing components, is to burn-in a fraction of the devices at a time at an elevated temperature and an increased voltage, in comparison with normal operation (normal operation is considered to be the usage of a device for non-test purposes, such as typical read/write operations). In order to fully burn-in all of the devices, each fraction of devices is burnt-in for a given period of time. The total time required to test an entire memory device is determined by multiplying the number of fractions the total number of components the device is broken down into by the time required to burn-in each component.